System for endodontic treatment

ABSTRACT

Provided is a system for endodontic treatment of a root canal. The system includes a handpiece containing a rotary motor adapted to rotate an endodontic file secured by the handpiece. A control unit executes a regime of motion of the motor to produce a regime of file motion in which episodes of oscillation of the file are separated by a rotation of the file. When the arc of a rotation is less than the arc of the oscillation that preceded the rotation, the arcs of the episodes of oscillation overlap and the formation of ridges in the root canal is avoided.

FIELD OF THE INVENTION

This invention relates to systems for endodontic treatment.

BACKGROUND OF THE INVENTION

Endodontic procedures require cleaning of the root canals and canalshaping. Proper cleaning and shaping of the root canals is a crucialfactor determining the success of the treatment. In shaping a canal, itis important that the canal wall be smooth and free of “ledges”.Cleaning and shaping of the root canal can be done manually using anendodontic file. Usually several endodontic files of different shapesand/or sizes are required to complete the procedure. Motor drivenendodontic files (rotary files) are also known. Rotary files aretypically tapered and have one or several helical fluted blades. Theusage of rotary files was initially limited to straight canals becausethe stainless steel files were not flexible enough to withstand rotationin curved canals. This situation changed with the development ofendodontic files made from Nitinol which have a flexibility about 6times higher than that of stainless steel files. Nitinol files canwithstand motor driven rotary operation even in curved canals.

Nonetheless the Nitinol rotary files are subjected to significantmechanical stress, and after prolonged use, material fatigue can causesudden breakage of the file without any prior visible deterioration ofthe file surface. Nitinol files have also been known to become jammedinside the canal and broken by excess torque applied by the motor. Thishas lead to the development of dental motors intended for endodontictreatments (“endomotors”) having a low rotational speed (usually 300 rpmto 1,000 rpm) and low torque (typically up to 6 Ncm) with torquecontrol, enabling stopping or reversing the file rotation when a presettorque limit is reached. Another problem associated with motor drivenfiles is self-threading of the rotating file into the canal due to thehelical blades on the file surface. The self-threading effect reducesthe dentist's ability to control axial advance of the file and may leadto over-instrumentation.

Dental motors with special reciprocating handpieces which generate arotary oscillation (reciprocation) of the file with a predetermined archave also been used. The reciprocating handpieces tend to reduce filebreakage caused by jammed files since deformation of the file remainswithin the resiliency limits of the Nitinol. The oscillating motionprevents self threading and improves control of the axial movement ofthe file. The arc of oscillation (usually 60° to 90°) tends, however, tocause unequal shaping of the canal walls and to create vertical ledgesin the canal wall, which impairs the outcome of the treatment. FIG. 2shows a cross-section of a tooth root 30 in which ledges 31 have formeddue to unequal shaping of the canal wall 32.

U.S. Pat. No. 5,944,523 discloses a motor assembly for root canaltreatment and other dental applications based on a stepping motor thatgenerates various movements of the file such as a continuous clockwiseor counterclockwise rotation, alternating movement and vibration withlow angular amplitude.

To achieve alternating movement of the endodontic file with anappropriate rotational speed (several hundred RPM) fast acceleration anddeceleration are required. A stepping motor, on the other hand, is onlycapable of generating a slow acceleration and deceleration. Furthermore,an alternating movement cannot provide full coverage of the root canalwall and will generate ledges.

U.S. Pat. No. 6,293,795 discloses a device in which clockwise rotationof the endodontic file of a relatively large arc alternates withcounterclockwise rotation of a smaller arc. In this way, the cuttingedges of the file pass over the entire surface of the root canalproviding complete coverage of the canal surface and the creation ofvertical ledges is prevented. The alternating movement of the file helpsto prevent file breakage and to reduce self threading, which is notcompletely eliminated since the forward arc of file rotation is alwayslarger than the reverse arc.

Root canals have different cross-section shapes which may be divided intwo categories: “round” canals and “flat” canals. FIG. 3 shows the crosssection of three roots 35, 36 37 having root canals 40, 41 and 42,respectively, that are essentially round in shape. FIG. 3 also shows thecross section of three roots 34, 38 39 having root canals 43, 44 and 45,respectively, that are essentially flat in shape. The broken circles inFIG. 3 show the cross section of the area cut by an endodontic file inrelation to the various root canals. It is important that during rootcanal cleaning and shaping the maximum surface of the root canal wallsbe covered. Shaping of a “round” canal is relatively simple sinceendodontic files with different diameters are manufactured and a file orsuccession of files optimally suiting a specific “round” canal may beselected for treatment. In case of “flat” canals, the situation is morecomplicated. The round cross-section of the area cut by an endodonticfile does not conform well to the elongated cross-sectional shape of thecanal leaving large areas of the canal walls untreated. It is possibleto “drive” the file along the flat surface of the canal wall so that thecutting edge of the file “shaves” the wall, but control of such movementis very difficult due to self-threading of the file. Moreover, suchpoorly controlled movement may easily cause jamming and breakage of thefile.

SUMMARY OF THE INVENTION

In one of its aspects, the present invention provides a system forendodontic treatment. The system of the invention a handpiece configuredto secure an endodontic file that is rotated by a motor. A control unithaving a microprocessor controls the motor in order to execute apredetermined or selectable regime of motion of the file. In oneembodiment, the regime of motion comprises the following stages:

(a) for k=1 to n, where n is an integer;

-   -   (i) oscillating the file from an angular position θ_(k) through        an arc α_(k) at a frequency of oscillation f_(k) for an amount        of time T_(k) or a number of oscillation cycles M_(k); and    -   (ii) rotating the file either clockwise or counterclockwise        through an arc β_(k).

In another embodiment of the invention, the microprocessor is configuredto execute a regime of motion comprising the following stages:

-   -   (i) rotating the file from an angular position θ_(k) through an        arc α_(k) at a angular speed ω_(k); and    -   (ii) rotating the file in an opposite direction through an arc        β_(k) wherein at least one of the sequences {α_(k), k=1 to n},        and {β_(k), k=1 to n} includes at least two terms of different        values.

The inventors have found that with a regime of file movement inaccordance with the invention, material fatigue of the file is reduced.A counter clockwise rotation between oscillations and/or reciprocationmotions has been found to reduce the self-threading of the file allowingmore precise control of axial file movement. Additionally it was foundthat file operation according to the invention enables improved controlof lateral file movement providing safe means for “shaving” of flatareas of a canal wall. In this mode of operation, the risk of filejamming and breakage during shaving is greatly reduced.

An unexpected benefit of the invention is low level of apical extrusion.During root canal shaping, the debris material should be removed fromthe canal towards the coronal part. However, some of the debriscontaining necrotic and contaminated tissues may be extruded through theapical foramen towards the periapical tissues (apical extrusion) causingpost-treatment complications. Root canal shaping with rotary instrumentsused in a rotation mode causes relatively low apical extrusion, whilethe apical extrusion using reciprocating techniques known in the art issignificantly higher. It was found that operation of a rotary fileaccording to the invention causes apical extrusion comparable with thatof regular rotary operation and much lower than the apical extrusion ofother reciprocation techniques.

Thus, in its first aspect, the invention provides a system forendodontic treatment comprising:

-   -   (a) a handpiece containing a rotary motor adapted to rotate an        endodontic file secured by the handpiece;    -   (b) a processor configured to execute a regime of motion of the        motor or produce a regime of file motion comprising:    -   (c) for k=1 to n, where n is an integer;        -   (i) oscillating the file from an angular position θ_(k)            through an arc α_(k) at a frequency of oscillation f_(k) for            an amount of time T_(k) or a number of oscillation cycles            M_(k); and        -   (ii) rotating the file either clockwise or counterclockwise            through an arc β_(k).

The system according to Claim 1 further comprising rotating the file ina continuous clockwise or counterclockwise rotation after completing oneor more steps (c).

β_(k) may be less than α_(k) for at least one k. α_(k) may be selectedfrom 60°, 90°, 120°, 180°, and 360°. M_(k) may be in the range of 1 to10. An angular velocity of the file during an episode of oscillation maybe in the range of 300°/sec to 2400°/sec. Any one or more of θ_(k),α_(k), f_(k), β_(k), T_(k) and M_(k) may be predetermined constants forall k, or any one or more of θ_(k), α_(k), f_(k), β_(k), T_(k) and M_(k)may be modulated. The modulation of any one or more of θ_(k), α_(k),f_(k), β_(k), T_(k) and M_(k) may be predetermined, or any one or moreof θ_(k), α_(k), f_(k), β_(k), T_(k) and M_(k) may be modulatedrandomly. Modulation of any one or more of θ_(k), α_(k), f_(k), β_(k),T_(k) and M_(k) may be modulated by a feedback mechanism involving anyone or more of a torque exerted on the file, depth of file penetrationinto a canal, file tip position relative to a canal apex, motortemperature, and elapsed time of treatment.

In another of its aspects, the invention provides a system forendodontic treatment comprising:

-   -   (a) a handpiece containing a rotary motor adapted to rotate an        endodontic file secured by the handpiece;    -   (b) a processor configured to execute a regime of motion of the        motor or produce a regime of file motion comprising:    -   (c) for k=1 to n, where n is an integer;        -   (i) rotating the file from an angular position θ_(k) through            an arc α_(k) at a angular speed ω_(k); and        -   (ii) rotating the file in an opposite direction through an            arc β_(k) wherein at least one of the sets {α_(k) for k=1 to            n}, and {β_(k) for k=1 to n} includes at least two terms of            different values.

The regime of motion may further comprise rotating the file in acontinuous clockwise or counterclockwise rotation after completing oneor more steps (c). The β_(k) may be less than α_(k) for at least one k.

The system according to any one of Claims 12 to 14 wherein αk isselected from 60°, 90°, 120°, 180°, and 360°. An angular velocity of thefile during an episode of rotation may be in the range of 300°/sec to2400°/sec. Any one or more of θ_(k), α_(k), ω_(k), and β_(k) arepredetermined constants for all k. Any one or more of θ_(k), α_(k),ω_(k), and β_(k), may be modulated. The modulation of any one or more ofθ_(k), α_(k), ω_(k), and β_(k), may be predetermined, or any one or moreof θ_(k), α_(k), ω_(k), and β_(k), may be modulated randomly. Themodulation of any one or more of θ_(k), α_(k), ω_(k), and β_(k), may bemodulated by a feedback mechanism involving any one or more of a torqueexerted on the file, depth of file penetration into a canal, file tipposition relative to a canal apex, motor temperature, and elapsed timeof treatment.

In another of its aspects, the invention provides a method for operatingan endodontic treatment system comprising a file, the method comprising:

(a) for k=1 to n, where n is an integer;

-   -   (i) oscillating the file from an angular position θ_(k) through        an arc α_(k) at a frequency of oscillation f_(k) for an amount        of time T_(k) or a number of oscillation cycles M_(k); and    -   (ii) rotating the file either clockwise or counterclockwise        through an arc β_(k).

The method may further comprise rotating the file in a continuousclockwise or counterclockwise rotation after completing one or moresteps (a). The βk may be less than α_(k) for at least one k. α_(k) maybe selected from 60°, 90°, 120°, 180°, and 360°. The number ofoscillation cycles M_(k) may be in the range of 1 to 10. An angularvelocity of the file during an episode of oscillation may be in therange of 300°/sec to 2400°/sec. Any one or more of θ_(k), α_(k), f_(k),β_(k), T_(k) and M_(k) are predetermined constants for all k. Any one ormore of θk, αk, fk, βk, Tk and Mk may be modulated. The modulation ofany one or more of θ_(k), α_(k), f_(k), β_(k), T_(k) and M_(k) may bepredetermined, or any one or more of θ_(k), α_(k), f_(k), β_(k), T_(k)and M_(k) may be modulated randomly. Modulation of any one or more ofθ_(k), α_(k), f_(k), β_(k), T_(k) and M_(k) may be modulated by afeedback mechanism involving any one or more of a torque exerted on thefile, depth of file penetration into a canal, file tip position relativeto a canal apex, motor temperature, and elapsed time of treatment.

In yet another of its aspects, the invention provides a method foroperating an endodontic treatment system comprising a file, the methodcomprising:

(a) for k=1 to n, where n is an integer;

-   -   (i) rotating the file from an angular position θ_(k) through an        arc α_(k) at a angular speed ω_(k); and    -   (ii) rotating the file in an opposite direction through an arc        β_(k) wherein at least one of the sets {α_(k) for k=1 to n}, and        {β_(k) for k=1 to n} includes at least two terms of different        values.

The method may further comprise rotating the file in a continuousclockwise or counterclockwise rotation after completing one or moresteps (a). The β_(k) may be less than α_(k) for at least one k. α_(k)may be selected from 60°, 90°, 120°, 180°, and 360°. An angular velocityof the file during an episode of oscillation may be in the range of300°/sec to 2400°/sec. Any one or more of θ_(k), α_(k), ω_(k), and β_(k)are predetermined constants for all k. Any one or more of θ_(k), α_(k),ω_(k), and β_(k), may be modulated. Any one or more of θ_(k), α_(k),ω_(k), and β_(k), may be predetermined, or any one or more of θ_(k),α_(k), ω_(k), and β_(k) may be modulated randomly. Modulation of any oneor more of θ_(k), α_(k), ω_(k), and β_(k), may be modulated by afeedback mechanism involving any one or more of a torque exerted on thefile, depth of file penetration into a canal, file tip position relativeto a canal apex, motor temperature, and elapsed time of treatment.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to understand the invention and to see how it may be carriedout in practice, embodiments will now be described, by way ofnon-limiting example only, with reference to the accompanying drawings,in which:

FIG. 1 shows a system of endodontic treatment in accordance with oneembodiments of the invention;

FIG. 2 shows a tooth root and root canal in which ledges have formed;

FIG. 3 shows tooth roots having circular and flat root canals;

FIG. 4 shows a regime of motion of an endodontic file in accordance withone embodiment of the invention; and

FIG. 5 shows a regime of motion of an endodontic file in accordance withanother embodiment of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1 shows a system 2 for endodontic treatment in accordance with oneembodiment of the invention. The system 2 comprises a handpiece 10 and acontrol unit 20. An endodontic file 11 is secured in a chuck of thehandpiece head 12. The handpiece 10 further comprises an electric motor14 fastened to a contra angle 13. The motor 14 is connected by a cable15 to the control unit 20 which includes a microprocessor 19, a memory21 a keyboard 16 and a display 17. The control system 20 controls themotor 14 in order to execute a predetermined or selectable regime ofmotion of the file 11, as explained below. In a cordless embodiment, thecontrol unit is incorporated into the handpiece 10 and the system isbattery operated. In another embodiment, the control unit isincorporated into the handpiece 10 and the system can alternate betweenbeing cordless or connected by a cable 15 to the host control/powersource/charger unit.

The memory 21 may be used to store operational parameters, such asspeed, torque, operational sequences, etc. of an endodontic treatment;as well as a library of operational parameters for different filesand/or file systems. The control unit 20 may include any one or more ofa non-volatile memory, wired or wireless communication channels, anInternet channel, data storage media, etc.

In accordance with the invention, the microprocessor 19 is configured toexecute a phase controlled regime of motion. In one embodiment, theregime of motion comprises the following stages:

(a) for k=1 to n, where n is an integer;

-   -   (i) oscillating the file from an angular position θ_(k) through        an arc α_(k) at a frequency of oscillation f_(k) for an amount        of time T_(k) or a number of oscillation cycles M_(k); and    -   (ii) rotating the file either clockwise or counterclockwise        through an arc β_(k).

FIG. 4 shows schematically an example of the regime of motions accordingto this embodiment for treating a root canal 50. The regime begins inFIG. 4 a with an oscillation of the file in an arc α₁=120°. At thetermination of M₁=10 oscillations, the file is rotated through an arcβ₁=60° and the file is then oscillated through an arc α₂=120° at the newlocation (FIG. 4 b) and after M₂=10 oscillations rotated through an arcβ₂=60° (FIG. 4 c). The process continues with oscillations of α₃=120°,M₃=5 (FIG. 4 c); α₄=120°, M₄=5 (FIG. 4 d); α₅=120°, M₅=3 (FIG. 4 e) andα₆=120°, M₆=3 (FIG. 4 d), interspersed with rotations β₃=60°, β₄=60°,and β₅=60°, as indicated in FIG. 4. Since β_(k) is less than α_(k) forall k, the arcs of oscillations for different k overlap (six overlappingoscillations of 120° are used to completely cover the entire 360°circumference of the canal), and the formation of ledges is thusavoided. Most endodontic files have more than one cutting edge (usually2 to 4) and the full coverage of the entire circumference of the canalcan be achieved in fewer steps.

Typically, the number of oscillation cycles M_(k) is in the range of 1to 10, and the angular velocity of the file during an oscillation stageis typically in the range of 300°/sec to 2400°/sec. β_(k) may be lessthan, greater than, or equal to α_(k). Setting β_(k) less than α_(k)ensures overlap of the coverage of the canal wall during consecutiveoscillation stages. α_(k) may increase with increasing k. For example,as shown in FIG. 5, a regime may consist of several oscillation stageswith α_(k)=60°, M_(k)=10 and β_(k)=60° (FIG. 5 a) followed byoscillation stages with α_(k)=90°, M_(k)=10 and β_(k)=90° (FIG. 5 b);then with α_(k)=120°, M_(k)=10 and β_(k)=120° (FIG. 5 c); α_(k)=180°,M_(k)=10 and β_(k)=120° (FIG. 5 d) and with α_(k)=360°, M_(k)=10 (FIG. 5e). The regime of motion may further comprise rotating the file in acontinuous clockwise or counterclockwise rotation after completing thereciprocation stages.

Any one or more of θ_(k), α_(k), f_(k), β_(k), T_(k) and M_(k) may bepredetermined constants for all k. or any one or more of θ_(k), α_(k),f_(k), β_(k), T_(k) and M_(k) may be modulated. The modulation may bepredetermined or random. The modulation may be determined during use bya feedback mechanism involving, for example, any one or more of a torqueexerted on the file, depth of file penetration into a canal, file tipposition relative to a canal apex, motor temperature, and elapsed timeof treatment.

As an example, in a preferred embodiment, when the torque applied to thefile exceeds a predefined value, any one or more of the arcs, frequencyor duration/number of oscillations can be modulated. For instance, theoscillation arc (α_(k)) and/or the oscillation frequency can be reducedand/or the number of oscillations (M_(k)) or the duration ofoscillations (T_(k)) can be increased. As another example, in preferredembodiment, when the file tip is advanced to a predetermined positionrelative to the apex, any one or more of the oscillation/reciprocationarcs, frequency or duration/number of cycles can be modulated, the motormay be stopped or reverse rotation can be activated, etc. For instance,when the file tip has reached the apical position, theoscillation/reciprocation frequency and the arcs may be reduced; audiofeedback may be activated, etc.

In another embodiment of the invention, the microprocessor 19 isconfigured to execute a regime of motion comprising the followingstages:

-   -   (i) rotating the file from an angular position θ_(k) through an        arc α_(k) at a angular speed ω₄; and    -   (ii) rotating the file in an opposite direction through an arc        β_(k) wherein at least one of the sequences {α_(k), k=1 to n}        and {β_(k), k=1 to n} includes at least two terms of different        values.

In a different embodiment the system may be combined with additionaldental devices, such as apex locator, vitality tester, fileidentification system, file working length measurement system, fileselection system, gutta-percha cutter, gutta-percha condenser,photo-polymerization lamp, trans-illumination lamp and others.

1.-42. (canceled)
 43. A system for endodontic treatment, comprising: (a)a handpiece containing a rotary motor adapted to rotate an endodonticfile secured by the handpiece; (b) a processor configured to execute aregime of motion of the motor or produce a regime of file motioncomprising: (c) for k=1 to n, where n is an integer; (i) oscillating thefile from an angular position θ_(k) through an arc α_(k) at a frequencyof oscillation f_(k) for an amount of time T_(k) or a number ofoscillation cycles M_(k); and (ii) rotating the file either clockwise orcounterclockwise through an arc β_(k).
 44. The system according to claim43, further comprising rotating the file in a continuous clockwise orcounterclockwise rotation after completing one or more steps (c). 45.The system according to claim 43, wherein the β_(k) is less than α_(k)for at least one k.
 46. The system according to claim 43, wherein α_(k)is selected from the group consisting of 60°, 90°, 120°, 180°, and 360°.47. The system according to claim 43, wherein the number of oscillationcycles M_(k) is in the range of from 1 to
 10. 48. The system accordingto claim 43, wherein an angular velocity of the file during an episodeof oscillation is in the range of from 300°/sec to 2400°/sec.
 49. Thesystem according to claim 43, wherein any one or more of θ_(k), α_(k),f_(k), β_(k), T_(k), and M_(k), are predetermined constants for all k.50. The system according to claim 43, wherein any one or more of θ_(k),α_(k), f_(k), β₁, T_(k), and M_(k), are modulated.
 51. The systemaccording to claim 50, wherein modulation of any one or more of θ_(k),α_(k), f_(k), β_(k), T_(k), and M_(k), is predetermined.
 52. The systemaccording to claim 50, wherein modulation of any one or more of θ_(k),α_(k), f_(k), β_(k), T_(k), and M_(k), are modulated by a feedbackmechanism comprising any one or more of a torque exerted on the file,depth of file penetration into a canal, file tip position relative to acanal apex, motor temperature, and elapsed time of treatment.
 53. Thesystem according to claim 50, wherein any one or more of θ_(k), α_(k),f_(k), β_(k), T_(k), and M_(k), are modulated randomly.
 54. A system forendodontic treatment, comprising: (a) a handpiece containing a rotarymotor adapted to rotate an endodontic file secured by the handpiece; (b)a processor configured to execute a regime of motion of the motor orproduce a regime of file motion comprising: (c) for k=1 to n, where n isan integer; (i) rotating the file from an angular position θ_(k) throughan arc α_(k) at a angular speed ω_(k); and (ii) rotating the file in anopposite direction through an arc β_(k) wherein at least one of the sets{α_(k) for k=1 to n}, and {β_(k) for k=1 to n} includes at least twoterms of different values.
 55. The system according to claim 54, furthercomprising rotating the file in a continuous clockwise orcounterclockwise rotation after completing one or more steps (c). 56.The system according to claim 54, wherein β_(k) is less than α_(k) forat least one k.
 57. The system according to claim 54, wherein α_(k) isselected from the group consisting of 60°, 90°, 120°, 180°, and 360°.58. The system according to claim 54, wherein an angular velocity of thefile during an episode of rotation is in the range of from 300°/sec to2400°/sec.
 59. The system according to claim 54, wherein any one or moreof θ_(k), α_(k), ω_(k), and β_(k), are predetermined constants for allk.
 60. The system according to claim 54, wherein any one or more ofθ_(k), α_(k), ω_(k), and β_(k), are modulated.
 61. The system accordingto claim 60, wherein modulation of any one or more of θ_(k), α_(k),ω_(k), and β_(k), is predetermined.
 62. The system according to claim60, wherein modulation of any one or more of θ_(k), α_(k), ω_(k), andβ_(k), are modulated by a feedback mechanism comprising any one or moreof a torque exerted on the file, depth of file penetration into a canal,file tip position relative to a canal apex, motor temperature, andelapsed time of treatment.
 63. The system according to claim 60, whereinany one or more of θ_(k), α_(k), ω_(k), and β_(k), are modulatedrandomly.
 64. A method for operating an endodontic treatment systemcomprising a file, the method comprising: (a) for k=1 to n, where n isan integer; (i) oscillating the file from an angular position θ_(k)through an arc α_(k) at a frequency of oscillation f_(k) for an amountof time T_(k) or a number of oscillation cycles M_(k); and (ii) rotatingthe file either clockwise or counterclockwise through an arc β_(k). 65.The method according to claim 64, further comprising rotating the filein a continuous clockwise or counterclockwise rotation after completingone or more steps (a).
 66. The method according to claim 64, whereinβ_(k) is less than α_(k) for at least one k.
 67. A method for operatingan endodontic treatment system comprising a file, the method comprising:(a) for k=1 to n, where n is an integer; (i) rotating the file from anangular position θ_(k) through an arc α_(k) at a angular speed ω_(k);and (ii) rotating the file in an opposite direction through an arc β_(k)wherein at least one of the sets {α_(k) for k=1 to n}, and {β^(k) fork=1 to n} includes at least two terms of different values.
 68. Themethod according to claim 67, further comprising rotating the file in acontinuous clockwise or counterclockwise rotation after completing oneor more steps (a).
 69. The method according to claim 67, wherein β_(k)is less than α_(k) for at least one k.